The present invention relates to medical electrical leads generally, and more particularly to implantable defibrillation electrodes and leads.
Early concepts of implantable defibrillators, such as disclosed in Reissue U.S. Pat. No. 27,652 by Mirowski, et al, envision an electrode system employing a ventricular endocardial electrode and a plate electrode mounted to the heart directly, subcutaneously, or to the skin. U.S. Pat. No. 3,942,536 by Mirowski, et al, discloses a transvenous lead having electrodes intended for location in the right ventricular apex and in the superior vena cava. This electrode system is disclosed as useful for either ventricular or atrial defibrillation. Such systems were eventually tested in human beings, with some success. Currently available implantable defibrillators typically employ epicardial or subcutaneous patch electrodes, alone, or in conjunction with one or more transvenous electrodes.
It is generally believed that it would be desirable to produce an implantable defibrillation system which entirely avoids the necessity of a thoracotomy, and there has been substantial work directed towards development of multi-electrode systems to accomplish this result, as disclosed in U.S Pat. No. 4,727,877 issued to Kallok, U.S. Pat. No. 4,708,145 issued to Tacker, et al, and as disclosed in U.S. Pat. No. 5,099,838, issued to Bardy. Other endocardial defibrillation electrodes are disclosed in U.S. Pat. No. 4,481,953 issued to Gold et al, U.S. Pat. No. 4,161,952 issued to Kinney, et al, U.S. Pat. No. 4,934,049 issued to Kiekhafer et al and in U.S. Pat. No. 5,042,143 issued to Holleman, et al. The Kinney, Gold, Holleman and Kiekhafer patents all disclose endocardial defibrillation leads employing defibrillation electrodes fabricated from elongated coils of biocompatible metal, mounted exposed to the exterior of the defibrillation lead, for location in the right ventricle and other locations within the heart. The above-cited Smits patent and the Mehra application both disclose a variety of endocardial defibrillation electrodes intended for use in the atrium, ventricle and coronary sinus, all of which employ electrodes taking the form of elongated coils of conductive biocompatible metals.
A return to lead systems employing only two electrodes for ventricular defibrillation is suggested in U.S. Pat. No. 4,922,927, issued to Fine et al. This patent proposes the use of an electrode system as in the above-cited Mirowski reissue Patent, using only a right ventricular electrode and a subcutaneous electrode, which may correspond to prior art subcutaneous electrodes or may be the metal enclosure of the defibrillator. The right ventricular electrode carries an elongated coil electrode fabricated of a copper-zirconium alloy coated with iridium oxide. The use of biphasic pulses in such a two electrode system is also recommended. However, no recommendation is given as to the preferred polarity for the leading phase of the biphasic pulse. The Fine patent states that ventricular defibrillation thresholds as low as 7-10 joules may be achieved with such an endocardial lead in conjunction with a subcutaneous electrode, apparently implanted in proximity to the ventricles, rather than pectorally. There is no suggestion to employ this electrode configuration for ventricular defibrillation.
Concurrent with the development of lead systems adapted to treat ventricular fibrillation, there has also been some work directed to the development of lead systems to treat atrial fibrillation. Synchronized cardioversion using two electrodes located on a lead located in the right atrium is disclosed in U.S. Pat. No. 3,738,370, issued to Charms. A later system is disclosed in U.S. Pat. No. 3,952,750, issued to Mirowski et al, employing one electrode in the atrium and presumably a second electrode at an unspecified location. Neither of these references discloses a specific embodiment for the electrodes located in the atrium.
An electrode lead system specifically designed for atrial defibrillation is disclosed in the article "Elective Countershock in Atrial Fibrillation With an Intracardiac Electrode--A Preliminary Report, by Jain, et al, published in the Journal of the Association of Physicians of India, Vol. 18, pp 821-824, 1970. This lead was provided with a 10 mm silver electrode for location in the right atrium and was tested in conjunction with either a second electrode located in the right atrium or a second, cutaneous electrode located on the left side of the chest wall. A second electrode system specifically designed for use in atrial cardioversion is disclosed in the article "Safety and feasibility of transvenous cardioversion in atrial tachycardia", by Blanc et al, published in Cardiac Pacing, edited by Gomez, Futura Pub. Co., 1985, pp 1526-1529. This electrode system employed a single lead with electrodes located in the atrium and pulmonary artery. More recently, the use of electrodes located in the right atrium and coronary sinus for atrial defibrillation has been disclosed in allowed U.S. patent application Ser. No. 07/661,568 by Mehra, filed Feb. 26, 1991, incorporated herein by reference in its entirety.